The human immunodeficiency virus (HIV) exerts profound cytopathic effects on the host T-lymphocyte following infection in vitro. The cytopathogenic properties of HIV in vivo may directly account for the depletion in circulating helper T4 lymphocytes and subsequent immune dysfunction which is the underlying cause of the acquired immune deficiency syndrome (AIDS). We hypothesize that superinfection -- unrestricted virus replication and buildup of a toxic viral gene product -- plays a crucial role in the process of viral cytopathogenicity. The process of superinfection itself may be directly influenced by biological properties of the host cell, i.e., surface receptor expression such that cells low in this receptor are not susceptible to virus mediated cytolysis. Thus, reduced receptor expression may directly modulate superinfection by preventing second round infection from progeny virus. We hypothesize that regulating viral replication will interfere with the process of viral superinfection, and the cytopathic effects of virus infection may be abrogated. In the proposed study, antisense viral RNAs will be used to confer cytopathicity resistance in susceptible host cells by restricting virus replication and thus prevent superinfection. Specifically, it is intended to: a) evaluate whether cells expressing antisense viral RNA can be protected from cytopathic effects of HIV infection. Inducible and constitutive expression vectors, containing HIV genes in antisense orientation will be introduced into HIV cytolysis susceptible cell lines. The ability of these cells to resist cytopathic HIV infection will be evaluated. To demonstrate the relationship between viral cytopathicity and the buildup of toxic viral gene products, the cytotoxic property of the envelope gene will be determined by overexpressing this gene in susceptible cell lines. b) investigate the dependence of viral cytopathogenicity and superinfection on the level of T4 receptor expression on the host cell, either by expressing the T4 gene in non-lymphoid cells in an attempt to confer susceptibility to viral cytopathogenicity or conferring cytolysis resistance in susceptible cells using antisense T4 RNA expression vectors. c) evaluate ability of retrovirus vectors expressing antisense HIV genes and synthetic antisense HIV oligonucleotides to protect human lymphocytes from cytopathic effect of HIv infection. Effectiveness of antisense RNA inhibition in restricting viral replication and cytopathicity in vitro may provide the rationale for the use of such an approach in vivo.